During a humoral immune response, resting B cells become activated, divide several times, and undergo terminal differentiation into plasma cells secreting different classes and subclasses of immunoglobulins. Frequently the change in the state of B cells, e.g. from resting to proliferating, from proliferating to secreting, or the like, can be correlated with changes in cell surface molecules, and these latter changes can be identified with monoclonal antibodies specific for the surface molecules or antigens; e.g. Zola, Immunol. Today, Vol. 8, pgs. 308-315 (1987). Such surface antigens can sometimes provide an approach for diagnosis and treatment, when a disease state is associated with the presence of cell types positive for particular surface antigens; e.g. Ramsay et al., Blood, Vol. 66, pgs. 508-513 (1985), "Autologous bone marrow transplantation for patients with acute lymphoblastic leukemia in second or subsequent remission: results of bone marrow treated with monoclonal antibodies BA-1, BA-2, and BA-3 plus complement" (treatment of common acute lymphoblastic leukemia (CALL) with antibodies specific for a CALL-specific antigen).
T cells are a class of lymphocytes essential for the activation of B cells during an immune response. Several important diseases are associated with depleted or non-functional T cell populations. At least two such diseases, AIDS and adult T cell leukemia (ATL), are caused by retroviruses, designated HTLV-III (now HIV) and HTLV-I, respectively; e.g. Broder et al., Ann. Rev. Immunol., Vol. 3, pgs. 321-336 (1985). ATL cells, like many other neoplastic cells, are associated with distinctive patterns of surface antigen expression, which sometimes provide a means for diagnosis or treatment; e.g. Jaffe et al., chapter 120, in Rose et al., eds., Manual of Clinical Laboratory Immunology, 3rd Ed. (American Society for Microbiology, Washington, D.C., 1986). Clearly, the identification of an additional surface antigen associated with particular disease states, and the development of monoclonal antibodies thereto, would improve available diagnostic protocols.